Ascending Projections to the Medial Geniculate Body from Physiologically Identified Loci in the Inferior Colliculus

  • M. S. Malmierca
  • A. Rees
  • F. E. N. Le Beau


The auditory thalamus, the medial geniculate body (MGB), possesses three main divisions: ventral (MGBv), medial (MGBm), and dorsal (Morest, 1964). The MGBv has a tonotopic organization (Aitkin and Webster, 1972; Imig and Morel, 1988, Morel et al., 1987, Wenstrup et al., 1994). In the guinea pig, low frequency regions are located in the caudal, dorsal and medial portions of the MGBv while high frequencies are represented in the rostral and lateral portions of the MGBv (Redies and Brandner, 1991). The main source of ascending input to the MGB is from the central nucleus of the inferior colliculus (CNIC; tree shrew: Oliver and Hall, 1972; cat: Andersen et al., 1980; Kudo and Niimi, 1980; Oliver, 1984; Rouiller and Ribaupierre, 1985; rat: LeDoux et al., 1987). These find- ings are based on large injections of HRP into the MGB, and injections of tritiated amino acids or WGA-HRP into the inferior colliculus (IC). They demonstrate unequivocally that the CNIC projects to the ventral and medial divisions of the MGB and that the projecting fibres terminate in a topographically ordered manner in the MGB. Dorsolateral regions of the CNIC project to the lateral parts of the MGBv while ventromedial regions of the CNIC project to the medial parts of the MGBv. This tectothalamic pathway originates from both disc-shaped and stellate cells (Oliver, 1984; Malmierca, 1991) and, at least four categories of axons ascending from the IC have been described in Golgi impregnated material of the cat MGBv (Morest, 1975). In the MGBv of the bat (Wenstrup et al., 1994) and ferret (Pallas and Sur, 1994) two types of terminal boutons associated with fibres from the CNIC have been observed following injections of biocytin into the IC or its brachium.


Auditory Cortex Inferior Colliculus Tree Shrew Primary Auditory Cortex Medial Geniculate Body 
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Copyright information

© Springer Science+Business Media New York 1997

Authors and Affiliations

  • M. S. Malmierca
    • 1
  • A. Rees
    • 1
  • F. E. N. Le Beau
    • 1
  1. 1.Department of Physiological SciencesThe Medical School University of Newcastle upon TyneUK

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